1. Technical Field
The present invention relates to a shift control device for a continuously variable transmission, and more particularly relates to a shift control device for a continuously variable transmission installed in a vehicle capable of switching over an engine output properties in accordance with driver operations.
2. Related Art
Continuously variable transmissions (CVTs), such as belt type CVTs and toroidal type CVTs, which can steplessly change the gear ratio, have come into widespread use in recent years as automotive automatic transmissions. A belt type continuously variable transmission includes a primary pulley provided to an input shaft, a secondary pulley provided to an output shaft, and a drive transmission component such as a belt or chain, wound over the pulleys. The gear ratio is steplessly changed by changing the groove width of the pulleys, thereby changing the diameter of the position where the drive transmission component rides.
The gear ratio of such continuously variable transmissions is controlled in accordance with parameters indicating the running state of the vehicle, such as accelerator position and vehicle speed, for example. This means that target engine speed (or target turbine speed, target primary pulley speed) are set based on these parameters, and the gear ratio is set such that the actual engine speed converges on the target engine speed.
Also, the continuously variable transmissions, in general, execute kick-down control (see Japanese Unexamined Patent Application Publication No. 2004-125072, for example), which is rapid acceleration control, in the case where the driver steps down on the acceleration pedal to request acceleration, and particularly in the case where the throttle position is around or beyond an intermediate position.
On the other hand, vehicles that enable the driver to switch an engine output properties according to preference have come into practical use in recent years. More specifically, vehicles have come into practical use that enable the driver to optionally select the engine output properties from three modes for example, which are a normal mode suitable for normal driving, a save mode (or economy mode) where output torque is suppressed to conserve gas mileage, and a power mode that give priority to power. This power mode exhibits output properties with good response from low speed through high speed (see Japanese Unexamined Patent Application Publication No. 2007-278266, for example).
Now, if a driver for example performs an operation during kick-down control of the continuously variable transmission (during rapid acceleration) to switch output properties (output mode) toward increased engine output (for example, an operation to switch from the above-described normal mode or save mode to power mode), it can be assumed that the driver desires to drive more aggressively. As such, it can be conceived to be desirable to enable the driver to physically feel the results of the switching operation regarding the engine output properties during kick-down more vigorously. However, the above-described conventional continuously variable transmissions have not taken into consideration giving the driver such a feeling of switching.